how to convert -2.5 into binary number?

i can convert 2.5, 2, -2 decimal values into binary number but when converting -2.5 binary output is same as 2.5 value,please help me

[Geoff Hayes]

What is the code that you are using to convert these numbers into binary?

[dpb]

What form of a binary number do you expect for a floating point value? IEEE-754 single, double, some other encoding????